1. Field of the Invention
The present invention relates to a magnetoresistive element (magnetoresistor) with an ordered double perovskite structure and a method for producing the same. More particularly, the present invention relates to a magnetoresistor which is an oxide crystal with an ordered double perovskite crystal structure, that has electrical conductivity, is enhanced in magnetic-conductance and spin-polarization characteristics, and is advantageously usable as a probe of a spin-polarization scanning type tunneling microscope or a magnetoresistor operable at room temperature, and to a method for the production of the oxide crystal.
2. Description of the Prior Art
An attention has recently been paid again to the physical properties of a transition metal oxide having a perovskite type crystal structure since the discovery of a high-temperature copper oxide superconductor. There have been made, for example, keen studies on a manganese oxide crystal in which a negative huge magnetoresistive phenomenon occurs. In conventional manganese oxide crystals, the magnetoresistive phenomenon has been remarkably observed particularly in a single crystal having no intergranularity.
In addition, there has heretofore been known an oxide with an ordered double perovskite type structure represented by the chemical formula of Sr.sub.2 FeMoO.sub.6 or Sr.sub.2 FeReO.sub.6. The crystal structure, magnetic property, etc. thereof have been studied, and it has been reported that the curie temperature thereof is in the vicinity of 400 K. that is much higher than room temperature. However, it has not been known that the oxide manifests a negative huge magnetoresistive effect.
Although it has been reported that the conventional manganese oxide single crystal manifests a negative magnetoresistive effect only in the vicinity of its magnetic transition temperature that is within a temperature range of room temperature to 2 K., there are few reports on an oxide ceramic that manifests a magnetoresistive effect over the entire temperature range and is easy to produce.
The present invention has been proposed in view of the above.
An object of the present invention is to provide a magnetoresistor that manifests a magnetoresistive effect over an entire temperature range.
Another object of the present invention is to provide a method for producing the magnetoresistor more easily than a conventional single-crystal producing method.